Prior to the present invention, combustion of lean gas and lean wet gas has been accomplished only with expensive equipment and most often very inefficiently. Low heat value gas is generally specified to have a heating value of approximately 150 Btu per cubic foot. Lean gas as contemplated herein may have a heating value as low as 35 to 90 Btu per cubic foot and some types of lean gas have a moisture content up to 45% by volume or higher.
A typical example of the expensive and complicated structures which have been suggested for the combustion of lean gases is shown in the French patent application of Continental Carbon Company, No. 7732829 based on patent application Ser. No. 757,532 filed in the United States by Karel R. Dahmen on Jan. 7, 1977, now U.S. Pat. No. 4,154,567. This application discloses an internal vane structure to create a vortex flow of the lean gas and also a swirling of the gases supplied to the auxiliary combustion supporting burner.
The L. P. Hine, Jr., et al U.S. Pat. No. 3,285,317 discloses a burner purporting to be a universal burner suitable for any type of gas and of relatively inexpensive sheet metal construction. The burner includes an elongate dished portion with a plurality of rows of slots therein with the slots nearest the manifold being of smaller width than the slots at the other end of the burner. Efforts to purchase a burner from the owners of this patent suitable for the burning of lean gases as defined above were not successful.
Others have suggested the use of slots in a burner but none have claimed to be able to burn lean wet gas. Examples of such prior structures are disclosed in U.S. Pat. No. 1,830,393 to B. A. Geurink et al (corrugated burner plate with slots at peak of corrugation ridges), U.S. Pat. No. 3,361,367 to G. Hein et al (alternating parallel long and short slots in burner plate) and U.S. Pat. No. 2,443,101 to J. H. Flynn et al (ribbon burner having two different size ports). The W. Flaskamp et al U.S. Pat. No. 3,106,955 discloses a vortex type of burner with a plurality of slots for entry of the air into the burner.